Corrosion inhibition



Patented May 26, 1 942 2 CORROSION INHIBITION James H. Werntz, Wilmington, DeL, assignmto E. I; du Pont de Nemonrs & Company, Wilmington, Del., a corporation of Delaware.'

No Drawing. Application May 13, 1939, Serial (01. roe-1 4) Claims. This invention relates to inhibiting the corresion of metals and particularly to inhibiting rust formation on ferrous metals due to the effect of moisture and oxygen.

Itis well known that the surfaces of metals, and'particularl the surfaces of ferrous metals, normally tend to corrode with the formation of rust when subjected to the .efiect of moisture and oxygen. Many methods have been proposed for preventing or inhibiting such corrosion and rust formation. One of the commonest methods proposed has comprised coating the metallic surfaces with a thin film of an oily material such as lanolin, Vaseline, and similar materials. While such oily materials are to some extent effective, they have not proved to be entirely satisfactory in practice.

It is frequently desirable to apply to metal surfaces, and particularly to ferrous metal surfaces including tin plate, lithographic inks, paints, lacquersand the like. When the metal surfaces are preserved with oily materials, it is generally necessary to remove such oily materials from the metallic surfaces prior to the application of lithographic inks, paints, lacquers and the like, as such oily materials greatly decrease the receptivity of the metal surface for inks, paints, lacquers and the like, and also decreases the retention of the inks, etc., on the metallic surfaces. This effect of the oily materials frequently goes so far as to prevent any application of the inks, etc., to the metal surface bearing the oily materials. When such oily materials are removed from the metal surfaces, the protective efiect of the oily materials is lost. Also, removal of the oily materials from the metallic surfaces involves an additional step requiring labor and expense.

It is a primary object of this invention to provide materials for coating metallic surfaces, particularly the surfaces of ferrous 'metals, which materials will be more effective for retarding corrosion and the formation of rust and at the same time will not decrease the receptivity of the metallic surfaces for lithographic inks, paints, lacquers and the like, or decrease the retentivity of such inks, etc., by the'metallic surfaces. Another object is to provide a method for treating metallic surfaces such as the surfaces of ferrous metals to inhibit corrosion of, and rust formation on, such metallic surfaces. A further object is to provide metals and particularly ferrous metals,

the surfaces of which will have a lesser tendency to be corroded and rusted, and which at the same time will have a high receptivity for, and retentivity of, lithographic inks, paints, lacquers and the like. Still further objects are to provide new compositions of matter and new articles of manufacture, and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accom-' plished in accordance with my invention, which comprises coating the surfaces of metals, and particularly the surfaces of ferrous metals, with a thin film of a composition containing an acyclic aliphatic acid-ester of a polycarboxylic acid, the acyclic aliphatic radical containing at least 6 carbon atoms and preferably long chains of from about 8 to about 18 carbon atoms. These acidesters may be otherwise designated-as those derived from a polycarboxylic acid and an acyclic aliphatic alcohol containing at least 6 carbon atoms. While it is preferred to employ the alkyl esters of the polycarboxylic acids, and particularly the esters which consist of the elements carbon, hydrogen and oxygen, either or both the aliphatic radical and the acid radical may contain substituents such as halogen, hydroxy, nitro, alkoxy, carboxyl or ester groups, as well as alkyl groups. Preferably, the acid is a dicarboxylic acid in which the two carboxyl groups are separated by at least two intervening carbon atoms. While the acids may be either aliphatic or aromatic, the aromatic acids are preferred and of these, I particularly prefer phthalic acid and its homologs.

I have found that the acid esters of my invention, when applied to metallic surfaces, and particularly to the surfaces of ferrous metals, in the form of a thin film, are very effective for retarding corrosion, particularly the formation of rust, of the metallic surfaces caused by moisture and oxygen. When such acid-esters are used as the sole coating substance, or are used in combination with other substances which do not decrease the receptivity of the metal for lithographic inks, paints, lacquers and the like or the retention thereof by the metals, then th receptivity and retentivity of the metal surfaces are not deleteriously affected but are, in some cases such as when phthalates are used, improved. In other words,

when the acid-esters of my invention, and particularly the phthalates, are employed in the absence of substances tending to reduce the receptivity of the metal surfaces for ink, lacquer, paint and the like, the metal surfaces can be lithographed, painted, lacquered or otherwise coated at least as successfully as they can be lithographed, etc. in the absence of a coating, without requiring removal of the acid-esters from the metallic surfaces prior to lithographing, painting, lacquen'ng, and the like. The long chain acid phthalates, such as the Lorol acid phthalates and dodecyl acid phthalate, are particularly effective for this purpose and materially improve the receptivity of the metal surfaces for lithographic inks, paints, lacquers and the like.

In other cases, where it is not proposed to lithograph, paint, or otherwise coat the metallic surfaces or where it i desirable to improve the corrosion protection at the sacrifice of paint and ink receptivity, the acid esters of my invention may be employed together with anon-volatile mineral, petroleum, vegetable or animal oil such as Vaseline," "NuJoP and lanolin. When my compounds are employed with such oils, it will generally be most practical and convenient to incorporate them in the oil prior to application to the metal surface. The use of such oils with my compounds will increase the protection against corrosion and rust formation, particularly where severe moisture conditions or corrosive gases are encountered. However, such oils will naturally be expected to decrease to a'xlarge extent the beneficial effects of my compounds on the receptivity and retentivity of the metallic surfaces for lithographic inks, paints, lacquers, and the like.

Although these compounds will usually be applied to metal surfaces by means of a solution using such well known processes as dipping,

spraying, wiping and brushing, it will be desirable at times to use other methods of application.

to a continuous coating at a suitabletemperature. The protective agent may also be emulsifled or dispersed in a liquid which is not a true solvent and applied to the metal surface in this form with subsequent evaporation of the carrier. In certain cases it may be advantageoustoprovide metal articles with a protective surface layer by permitting the condensation of vapor from one of these compounds upon the metal surface.

When solvents are employed, they may be of any desired concentration. However, it will'generally be undesirable to use solutions of more than 15% concentration. The, preferred solutions for most purposes will usually have a concentration of from about 1% to about 8% ,of the acid-ester. The film of material will preferably be of such thickness as will be obtained by the coating of from 10,000 to 80,000 square feet of surface with one pound of ester or anti-corrodent composition. Solutions of 1 to 8% concentration will generally provide such thickness of Amongst the compounds of my invention which are particularly desirable are:

Dodecyl acid phthalate "Lorol acid phthalate Octadecenyl acid phthalate Castor oil acid phthalate octadecyl acid phthalate octadecyl acid maleate Alcohol em 10 ed in making this compound was a mixture of norm l prime monoh dric aliphatic alcohols obtained b the carboxy c reduc on of coconut oil; This mixture 0 alcohols is known to the trade as Lorol alcohol. The resultln product is a mixture of the acid phthalate esters of su alcohols.

sheets.

In order to illustrate more clearly the preferred modes of carrying my invention into eflect, the

following examples are given:

. Example 1 Cold rolled 20-gauge steel sheet is prepared for storage and shipment by cleaning in a vapor degreaser, immersing brieflyin a 4% solution of dodecyl acid phthalate in toluol, draining and drying at room temperature.

' Example II tween cloth rolls saturated with a 3% solution of Lorol acid phthalate in Xylol. The solvent evaporates readily during a short travel on belt conveyors and the sheets are then inspected and stacked for packaging. After six weeks storage in an industrial atmosphere, exposed to average condensation conditions, untreated control sheets were badly rusted. Steel sheets coated with lano lin in this manner showed comparatively large rust spots uniformly distributed over each sheet. on the other hand, steel sheets treated as above were rust-free with the exception of very small rust spots scattered along the outer edges of the Example III Iron wire is drawn in the usual manner and, after leaving the last die, the wire is passed between felt pads impregnated with octadecenyl acid phthalate. A treatment of this type does not affect the appearance of the wire, but will prevent rust formation over extended periods of storage.

Example IV Wire nails are fabricated and burnished in the usual manner, after which they are basket dipped in a solution comprising 2% octadecyl acid maleate and 10% light mineral oil in low flash naphtha. The nails are then drained and dried by tumbling in a current of warm air. Such products are especially suited for the export trade because of their resistance to corrosion induced by salt air.

In order to show further the effects of my compounds, and particularly in relation to some related compounds not within my invention, the results of a number of tests are given in the following tables, in which control" refers to similar untreated steel panels subjected to the same conditions as the treated steel panels:

Table I Com- Agent parative Observations on rusting rating 3 Heavy continuous rust. 3 Do. 3 Do. I 9 Very alight rust in isolated s Didodecyl maleate 6 MRS, rust s ts. Dibutyl maleate 3 Heavy cont uous rust. Castor 011 sold phthalate..- 8 Slight scattered rust spots.

The rating as here given is an arbitrary figure which is based on the figure 10 for complete absence of rufiing and 0 for complete rustingover the whole surface of the panel.

. 2,284,241 3 Table I! ployed in preparing suitable compounds of my invention. The following agents were applied on bright Alcohols Acids steel panels to a thickness of 0.1 mil by rubbing gex l g mmm l i i the agent on the steel. The treated panels were 5 gg gg 'gg g am," then exposed to outdoor weathering for a period Myrialgll Trimethylsuccinic 8 d Tet ecyl. Phen lsucclnic of 1 Dodeoyl Mac a Octadecyl Phenyl maleic Linoleyl gall-lo Agent Rating Observations on rusting 10 gggf g "2 0ml" Adipic NujoY' 0 Completely covered with c g fi g $23 Control o ga ethylcyclohexyl Ultra-conic Dodecyl acid phthalate--." a v slight scattered rust gggggagg wig- Egg Octadecyl acid phthalateuu s Slight scattered rust spots. 135 22??? fia ggg g Alcohols of 6 or more carbon o-Carboxyhydrocinnamic swwmwmw gzsieaesrzae 3.1%.

Homologs and isomers of above Naphthalic Table III Diphenic r 1 lf l li llt isl ed l i t l l 1 1 llthalc 0 B. C0 0 S D e [0 p l The following agents w pp 11 bright catalytic reduction 0 the Halogenophthali steel panels by dipping in a 2% toluene solution fatty acids from sperm oil. Alky ated phtha 1c and home- (except where otherwise indicated) and, after removal of the solvent by evaporation, exposing the panels to continuous water condensation for seven days: 25

Agent I Rating u m Nonyl acid phthalate.

Dodecyl acid dphthalate Castor oil aci phthalate Cellulose acid phthalate (56% Solution in toluene None (control) Diethyl citrate Acid phthalate oi the alcohols of seven and eight carbon atoms obtained by the hydrogenation of carbon oxides...

Dii yl mrnlatn Stcaryl acid phthalate Agent Rating None (control) 1 Lanolin 5 Stearyl acid phthalate 8 The examples and tests hereinbefore given merely illustrate the results obtained with some of the compounds of my invention. Other desirable compounds of my invention are;

Lorol acid nitrophthalate Octyl acid phthalate Cetyl acid phthalate logs and isomers oi the above Still other compounds within my invention may be obtained from alcohols obtained by the oxidation of petroleum, or by the reduction of the acids obtained from petroleum or from the oxidation of petroleum. Further, mixtures of two or more of the above esters, mixtures obtained by reacting any one of the acids with a mixture of any of the above alcohols and mixtures obtained by reacting any one of the above alcohols with a mixture of two or more of the above acids may be employed.

My compounds may be used for the temporary protection of metal which is to be fabricated further, such as steel sheet, wire and tubing, or may be used in treating finished articles such as machine parts, tools, guns, locks, and the like. These compounds are also particularly well adapted to the protection of ferrous metal articles such as bolts, nuts, nails, bearings, cutlery, gears, metallic cases, and the like. They may also be used for the treatment of ferrous metal articles which have been provided with a surface coating of some other mineral or alloy such as chromium, copper, nickel, cadmium, zinc, brass, aluminum, tin, lead, etc. In addition, these compounds may be applied to the surfaces of other metals and alloys, particularly those used for structural shapes and articles of commerce. Among such metals are zinc, brass, bronze,

aluminum, tin, copper, pewter, lead, magnesium,

cadmium, nickel, duralumin, and the like.

My compounds are definitely more effective in inhibiting corrosion due to moisture condensation than equivalent amounts of. such commonly used materials as wool fat and mineral oil. The principal advantage of my compounds over the former type of compound isrealized when the treated metal surface is to be painted or lithographed subsequently. Neither wool fat nor mineral oil can be tolerated on a metal surface which is being lithographed, painted or lacquered, while my compounds, and particularly the Lorol" acid phthalate and dodecyl acid phthalate, actually I improve the ink and paint receptivity of the metal surface and promote the flow and leveling of the applied ink, paint, lacquer or the like. Thus, instead of necessitating an expensive degreasing operation as is generally necessary with the heretofore proposed oily materials, the protection of the metal surfaces with the compounds of my invention produces a better lithographing and painting base and is of material assistance in the The following alcohols and acids may be emfinishing operations on many manufactured articles without requiring the use of a de'greasing or equivalent operation.

While I have disclosed the preferred embodiments of my invention and the preferred modes 01' carrying the same into eflect, it will be readily with a thin film consisting of an aliphatic acidester of a polycarboxylio acid, in which the allphatic radical is a member of the group consisting of acyclic aliphatic, cyclohexyl and naphthenyl radicals and contains at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

2. A ferrous metal having its surface coated with a thin film consisting of an acyclic aliphatic acid-ester of a dicarboxylic acid in which the carboxyl groups are separated by at least 2 intervening carbon atoms, the acyclic aliphatic radical containing at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

3. A ferrous metal having its surface coated with a thin film consisting of an acyclic alkyl acid-ester of a dicarboxylic acid in which the carboxyl groups are separated by at least 2 intervening carbon atoms, the acyclic alkyl radical containing at least 8 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

4. A ferrous metal having its surface coated with a thin film consisting of an acyclic .aliphatic acid-ester of a phthalic acid in which the acyclic aliphatic radical contains at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen. 4

5. A ferrous metal having its surface coated with a thin film consisting of an acyclic alkyl acid-ester of phthalic acid in which the acyclic alkyl radical contains at least 6 carbon atoms.

6. A rust-proofing composition for metals consisting of a solution, in an inert volatile solvent, of an aliphatic acid-ester of a polycarboxylic acid, in which the aliphatic radical is a member of the group consisting of acyclic aliphatic, cyelohexyl and naphthenyl radicals and contains at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

' consisting of a solution,

7. A rust-proofing composition for metals consisting of a solution, in an inert volatile solvent, of an acyclic alkyl acid-ester of a dicarboxylic acid in which the carboxyl groups are separated by at least 2 intervening carbon atoms, the acyclic alkyl radical containing at least 8 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

8. A rust-proofing composition for metals consisting of a solution, in an inert volatile solvent, of an acyclic alkyl acid-ester of a phthalic acid in which the acyclic alkyl radical contains at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

9. A rust-proofing composition for metals consisting of a, solution, in an inert volatile solvent, of an acyclic aliphatic acid-ester of phthalic acid in which the acyclic aliphatic radical contains at least 6 carbon atoms, said ester consisting of the elements carbon, hydrogen and oxygen.

- 10. A ferrous metal having its surface coated with a thin film consisting of the acid phthalates of the mixture of normal primary monohydric aliphatic alcohols obtained by the carboxylic reduction of coconut oil.

11. A rust-proofing composition for metals in an inert volatile solvent, of the acid phthalates of the mixture of normal primary monohydric aliphatic alcohols obtained by the carboxylic reduction of coconut oil.

12. A ferrous metal having its surface coated with a thin film consisting of the acid maleates of the mixture of normal primary monohydric aliphatic alcohols obtained by the carboxylic reduction of coconut oil.

13. A ferrous metal having its surface coated with a thin film consisting of stearyl acid phthalate.

14. A rust-proofing composition for metals consisting of a solution, in an inert volatile solvent, of the acid maleates of the mixture of normal primary monohydric aliphatic alcohols obtained by the carboxylic reduction of coconut oil.

15. A rust-proofing composition for metals consisting of a solution, in an inert volatile solvent, of stearyl acid phthalate.

JAMES H. WERNTZ. 

